1. Field of the Invention
The present invention relates to a vehicular operation switch, which includes a light source illuminating a switch knob from a rear face side, and which includes a grease that is applied to a sliding part.
2. Description of Related Art
Most of devices placed in a passenger compartment, such as a navigation system, a display, an audio system, and an air conditioner, include a light source illuminating a switch knob from a rear face side of the switch knob so that the vehicular operation switch has better visibility in the night. For example, Japanese Patent Laid-Open No. 2001-222924 bulletin discloses a vehicular operation switch that includes a light source illuminating such a switch knob from the rear face side of the switch knob.
Because, the vehicular operation switch is used frequently by a vehicle user, the touch (feel) and quality of the switch knob in the press operation are regarded as important. Because of this, a clearance in a sliding part of the switch knob during the press operation is designed to be as small as possible such that a wobble of the switch knob in the press operation is limited. Also, as for the many vehicular operation switches, a grease is applied to the sliding part such that the touch and quality of the switch knob during the press operation are improved.
As explained above, the touch of the switch knob, which includes the grease applied to the sliding part, during the press operation is good and has high quality. In contrast, a viscosity of the grease is prone to rise in accordance with a decrease of temperature, in general. Because of this, the viscosity of the grease applied to the sliding part rises when the vehicle is left unattended for a long time under an extremely low temperature environment of a cold district. Thus, the force that is necessary for the press (push) of the switch knob increases in the operation switch. In a worst case, the grease may freeze so that the switch knob becomes unable to be pressed.
Firstly, the vehicle user starts the engine of the vehicle, which has been left under the extremely low temperature environment for a long time. Then, when the air conditioning heater raises the vehicle indoor temperature to about a normal temperature, the viscosity of the grease recovers to that corresponding to the normal temperature. Therefore, the operational feel of the vehicular operation switch becomes normal. However, because the passenger compartment is very large, it generally takes a long time to raise the vehicle indoor temperature. Also, in a case, where the vehicular operation switch for turning on the air conditioning heater is frozen while the air conditioning heater is not activated, the air conditioning heater cannot be turned on. Therefore, the vehicle user will disadvantageously feel unpleasant for a long time.